only delete c from nr once

1 files changed, 5 insertions, 3 deletions

diff --git a/challenge-074/walt-mankowski/python/ch-2.py b/challenge-074/walt-mankowski/python/ch-2.py
index 1c1d4e1609..e80b5b0246 100644
--- a/challenge-074/walt-mankowski/python/ch-2.py
+++ b/challenge-074/walt-mankowski/python/ch-2.py
@@ -1,7 +1,7 @@
 from sys import argv
 
 s = argv[1]
-seen = set()
+seen = {}
 nr = []
 out = []
 
@@ -9,11 +9,13 @@ for c in s:
     # have we seen c before?
     if c not in seen:
         # add c to nr
-        seen.add(c)
+        seen[c] = True
         nr.append(c)
     else:
         # remove c from nr
-        nr.remove(c)
+        if seen[c]:
+            nr.remove(c)
+            seen[c] = False
 
     # now the FNR is either the last element of nr, or #
     out.append(nr[-1] if nr else '#')